This invention relates generally to high vacuum steam sterilization processes which heat sterilize articles such as medical container closures. More specifically, it relates to the sterilization of bagged closures such as vial stoppers and caps used in the pharmaceutical industry.
In order to accomplish the removal or destruction of all living organisms from objects, high vacuum steam sterilization provides an effective infection and contamination control in pharmaceutical environments. Sterilizers of this type safely and efficiently accomplish sterilization by utilizing saturated steam as the sterilant. The saturated steam is a gas and is therefore able to circulate by convection which allows the steam to penetrate porous objects in the sterilizer. This permits the efficient sterilization of a quantity of small parts which are delivered for sterilization in permeable bags. Small container closures such as elastomeric stoppers are used in high volume by the pharmaceutical industry and the efficient sterilization of these items is required. These parts are sealed in bags having a permeable membrane and are delivered packaged this way to a steam autoclave for sterilization. By way of example, the sterilizable bags may be of the type sold under the name Steribag(trademark) by the West Company of Lionville, Pa.
A problem exists however because the bagged stoppers are sealed in the bags directly after washing without being dried. Thus, the stoppers are still wet from washing and therefore the bags contain a significant amount of water. Hence, the stoppers need to be dried as well as sterilized before they can be delivered to installation equipment which applies the stoppers to individual containers such as serum vials which hold the pharmaceutical products.
To sterilize bagged items such as the pharmaceutical closures which are the specific subject of the present invention, a vacuum autoclave must be used because air trapped in the bag must first be removed since it inhibits the process of steam sterilization. To achieve air removal, a vacuum steam autoclave typically subjects its contents to a conditioning or prevacuum phase in which the autoclave environment undergoes a series of alternating vacuum and steam cycles to remove air from the autoclave and the interior of the stopper bags. Three or four pulses are usually employed, each drawing a vacuum on the autoclave chamber and then introducing steam until the chamber reaches a predetermined positive pressure when the admission of steam is stopped and a vacuum is once again drawn. This type of pulsing is known to provide the greatest efficiency in quickly effecting the desired removal of air prior to sterilization. As described above, however, this conditioning process can actually add water to the interior of the sterilizable bags which adversely affects the duration of the drying cycle after sterilization.
Drying is normally accomplished by simple hot air convection at the end of the sterilization process. However, the steam sterilization process can be problematic to the drying cycle of bagged items because the steam can add water to the bag of stoppers if there is condensation of the steam. This further increases the drying time after sterilization which can take as long as eight hours for the total sterilization/drying process. Simply increasing the heat to speed the drying process is not a viable solution because the dry heat can be destructive to the elastomeric stoppers causing a deterioration in their elastomeric tensile strength, elongation, and durometer hardness.
Prior art patents of which the applicant is aware include U.S. Pat. No. 4,309,381 issued to Chamberlain et al. which discloses methods for establishing and ascertaining air removal in steam sterilization, however there are no teachings which address the problem or propose a solution to removing water content from small bagged articles. U.S. Pat. No. 4,759,909 issued to Joslyn discloses the use of air removal by subjecting the goods to a plurality of pressure pulses at above atmospheric pressure by alternate pressurization and venting of the chamber to atmospheric pressure during which air is removed from the chamber with steam prior to pressurized sterilization. There is, however, no teaching of admitting air during the pressure pulses while drawing a vacuum on the chamber during the air removal phase. The Joslyn patent does not address the problem of removal of water from materials or the problem of water content in sterilization bags of bagged articles. There is therefore a need in the art to accomplish the combined sterilization/drying process for bagged pharmaceutical closures more quickly and without having a destructive effect on the performance of the closures.
According to the present invention, a sterilization process for bagged articles as will be described more specifically with regard to the description of the preferred embodiment, a novel approach is taken with regard to the conditioning or air removal phase prior to sterilization. This has shown to not only prevent the addition of water to the sterilizable bags during this phase but in fact to remove 90 percent of the liquid moisture. This is accomplished by introducing brief periods of dry warm air to the autoclave chamber at the point of greatest vacuum during the prevacuum pulsing. It is contrary to logic to introduce air during the air removal phase when the objective is to remove air, however this method has shown surprising and unexpected results. While it is not fully understood why the present system works so effectively, it is believed that this timed admission of warm air during the conditioning pulse cycles maintains the temperature of the stoppers above their condensation point and also increases the mass of vapor flowing through the vacuum pump with the purging air being used as the transport medium for the condensable vapor. Thus, the liquid water in the product bags becomes greatly reduced.
More specifically, the applicant has invented a method of conditioning and sterilizing materials such as bagged vial stoppers comprising the steps of first placing the materials into a sealed vacuum steam autoclave chamber and then removing air from the chamber during an air removal phase by admitting steam into the chamber and initiating a series of vacuum pulses by a vacuum pump. The pulses include successive pressure-down and pressure-up segments between which air is injected into the chamber for a brief period while the chamber is maintained at below atmospheric pressure by the vacuum pump. The air is injected into the chamber through an air supply valve which is rapidly opened and closed to supply short bursts of air into the chamber while the chamber is maintained within a pre-selected pressure range between the successive pressure-down and pressure-up segments. The injected air is preferably heated and dried prior to being supplied into the chamber. After the air removal phase is complete, the materials are sterilized by introducing steam into the chamber for a period of time sufficient to effect sterilization. The step of sterilization is followed by a drying step where the bagged vial stoppers are dried with hot air while the chamber is held below atmospheric pressure.
The invention will be more clearly understood by those of skill in the art from the following drawings and description of the preferred embodiment. While the present invention will be described with reference to a specific embodiment, the description is illustrative of the invention and is not to be considered as limiting the invention. Various modifications to the invention can be made to the preferred embodiment by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.